The present invention relates to the transportation of granular materials and more particularly to an improved method and apparatus for the pneumatic transportation of granular material in both dry and wet form.
The term "granular material" as used herein refers to particulate materials ranging in particle size from finely divided dust and powders to coarse gravels and includes mixtures of particulate materials such as for example refractory mixes, sand and cement mixes and the like. In construction work such materials are frequently pneumatically transported to a work site where an activating fluid, such as water in the case of sand and cement, is introduced to a stream of the granular material to form a cementitious construction material which is distributed, or "gunned" over a surface or into a suitable form and left to harden. In other cases, pneumatic means are employed for merely transporting the granular material from one point to another.
Mechanisms for effecting pneumatic transportation of granular materials are known in the art and generally comprise a hopper or storage area for the granular material, a pneumatic discharge area for entraining the granular material in an air stream and a feed mechanism for conveying granular material from the hopper to the pneumatic discharge area. A highly efficient device of the type to which the present invention generally relates is disclosed in U.S. Pat. No. 3,161,442. This device includes, in addition to the hopper and pneumatic discharge area, a rotatable feed rotor which is provided with a plurality of pockets for receiving increments of granular material from the hopper. The pockets are moved by rotation of the feed rotor into registration with an air discharge line in the pneumatic discharge area for the entrainment of the granular material in an air stream.
The prior art devices required granular materials having good flow characteristics in order to properly function and often the presence of even minor amounts of moisture is sufficient to cause stoppages or to otherwise produce a discontinuous, non-uniform stream. Such conditions are undesirable, particularly where the device is used for gunning concrete since variations in the discharge stream can adversely affect the ultimate properties of cement. In addition, it is preferred in some construction work and the like to premix the granular material and liquid, although for gunning operations using pneumatic transporters, premixing to form a wet mix having the most desirable ultimate properties is very difficult because of the poor flow characteristics of the mix.
Furthermore, unintentional additions of moisture such as exposure to the elements often result in blockages requiring shutdown and disassembly to clear the blockage.
The present invention overcomes the foregoing deficiencies of the prior art and provides for the pneumatic transportation of granular material having poor flow characteristics. Further the present invention permits the pneumatic transportation of premixed granular material and activator liquid in proportions which heretofore were considered as being non-transportable by pneumatic means.